1. Field of the Invention
The present invention relates to an optical light guide member for guiding incident light from an annular light incident end surface formed at one end of a tubular portion such that the light is emitted from a light exit surface extending along a flat surface intersecting an axis of the tubular portion, and to an illumination unit and an instrument in which the foregoing optical light guide member is assembled.
2. Description of the Related Art
For illumination for an instrument in a speedometer of an automobile in prior art techniques a light source is provided on an outer circumference of an indicator section to illuminate the indicator section or a light source is provided on the backside of the indicator section having a transparent portion through which light transmits to achieve transmission illumination for the indicator section. In these prior art techniques use is however made of a light bulb as the light source.
A light bulb for use in illumination for an instrument equipped in an automobile has a problem in durability against vibration and so on, followed by relatively much consumption of electric power and by difficult exchange of any light bulb when it burned out.
For illumination of the type where light from a light bulb is directly applied to the surface of the indicator illumination efficiency is deteriorated to the utmost at locations far away from the light bulb even if the configuration of a reflector is designed variously, so that it is necessary to arrange a plurality of light bulbs along an outer circumference of the indicator, to result in such inconvenience that the consumption of electric power for illuminating the indicator is increased.
Although in the type of the transmission illumination as described above such inconvenience is moderated, in order to uniformize the light transmitted through the indicator it is necessary to increase a distance from the indicator to the light source, obstructing the instrument to be made compact.